The present invention relates to an electromagnetic actuator of an improved type for controlling the valves of an internal-combustion engine.
As is known, experiments are currently being carried out on internal-combustion engines, wherein the valves for induction and exhaust which put the combustion chamber of the engine selectively into communication respectively with the induction manifold and the exhaust manifold of the engine, are actuated by electromagnetic actuators, which are piloted by an electronic control system. This solution makes it possible to vary very accurately the lifting, opening time, and moments of opening and closure of the valves, according to the angular speed of the crankshaft and other operating parameters of the engine, thus increasing substantially the performance of the engine.
The electromagnetic actuator which provides the best performance at present is disposed adjacent to the stem of the valve to be moved axially, of the internal-combustion engine, and comprises:
support frame which is integral with the head of the internal-combustion engine;
an oscillating arm made of ferro-magnetic material, which has a first end pivoted on the support frame, such that it can oscillate around an axis of rotation which is perpendicular to the longitudinal axis of the valve, and a second end in the shape of a cam, which abuts the upper end of the stem of the valve; and
a pair of electromagnets, which are disposed on opposite sides of the central portion of the oscillating arm, such as to be able to attract the oscillating arm by command and alternately, making it rotate around its axis of rotation.
Finally, the electromagnetic actuator comprises two resilient elements, which can keep firstly the valve of the engine in the position of closure, and secondly the oscillating arm in a position such as to keep the same valve in a position of maximum opening. These resilient elements act in opposition with one another, and have dimensions such that when both the electromagnets are not being supplied, i.e. when they are in a condition of equilibrium, the elements can position the oscillating arm in a position of rest, in which the latter is substantially equidistant from the polar heads of the two electromagnets, such as to keep the valve of the engine in an intermediate position between the position of closure and the position of maximum opening.
The main disadvantage of the above-described electromagnetic actuator is that it has mechanical play between the end in the shape of a cam of the oscillating arm, and the upper end of the stem of the valve, which varies substantially according to the temperature of use of the actuator, thus to some extend eliminating the advantages derived from the use of an electromagnetic actuator of this type. In fact, the lifting of the valve, the opening time, and the moments of opening and closure of the valves vary substantially according to the mechanical play which exists between the end in the shape of a cam of the oscillating arm, and the upper end of the stem of the valve, thus reducing substantially the accuracy of actuation which can be obtained by the said electromagnetic actuator.
The object of the present invention is to provide an electromagnetic actuator for controlling the valves of an internal-combustion engine, which is free from the above-described disadvantages.
According to the present invention, an electromagnetic actuator of an improved type is provided, for controlling the valves of an internal-combustion engine, comprising a head, at least one combustion chamber with a variable volume, at least one connection pipe which can put the said combustion chamber into communication with the exterior, and at least one valve which can regulate the passage of fluids from and towards the said combustion chamber; the said valve being fitted such as to be axially mobile in the head, between a position of closure in which it shuts the said connection pipe, and a position of maximum opening, in which it permits the passage of the fluids through the connection pipe, with the maximum flow rate permitted; the said electromagnetic actuator being fitted on the head, in order to move the said valve by command, between its position of closure and its position of maximum opening, and being characterised in that it comprises means for recovery of the mechanical play which exists between the said valve and the actuator itself.